WiFi non-ISP router/modem presence or motion detection experiences?

i saw this: sciencedaily.com/releases/2026/08/260811052857.htm and saw this post by the author of Tommy but it requires ESP devices: i’m hoping to buy a router/modem that’s not controlled by my ISP and then also be able to avoid buying mmWave or motion sensors to sort out when someones home and this seems like a great approach That said I have no experiences in any of these optipns, is this a crazy thought? is it even possible?